Change to Herrick's...Machine

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <kcha1-at-juno-dot-com>

To those who have obtained the documentation for my Entertainment
Machine:

Another small improvement...  In dwg TCG-CK1A (main circuit), I've
changed the two MOSFET driver transistors A2Q2 and A2Q3 to
ZTX949's--having a 4A Ic rating.  Also, I've added a Schottky diode
between each base and collector, with cathode to base--Digi-Key no.
31DQ05.

Two purposes:  First, to boost the current capability of the transistor. 
If one of the transistors opens up, then one or more current-ring MOSFETs
will fry, a fuse will blow, & very likely the associated regulator MOSFET
will fry.  Such a bore.  Second, the Schottky diode keeps the transistor
acting like a transistor even when the seriesed collector diodes open up
on negative half-cycles.  That protects the b-e junctions against
possible excessive current.

I've been working on trying to improve the off-line power supplies'
voltage regulation, so far with no particular success since I want to
keep them simple.  The present circuit is a very simple-minded and
conventional "buck" type.  I've breadboarded a "buck/boost" configuration
but it's worse, so far, as to voltage regulation; and also, its MOSFETs
have to keep switching all the time which tends to warm them up a bit
much.  So, still working on it...

Ken Herrick
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